[R] Performance difference between 32-bit build and 64-bit bu ild on Solaris 8

[Peter Dalgaard]

Scott Gilpin <sgilpin at gmail.com> writes:

> Andy, Prof. Ripley - thanks for your replies.
> 
> > CFLAGS was not specified, so should default to "-g -O2".  It is definitely
> > worth checking, although almost all the time in these tests will be spent
> > in Fortran code.
> Yes - I verified that's the default.
> 
> > >> neither build uses a BLAS.
> > 
> > Well, they do, the one supplied with R (which is in Fortran).
> 
> I guess I should have said that neither build is using an optimized
> BLAS.  (which I am planning to install - I just haven't had the chance
> yet.)   I also get a message in config.log "ld: fatal: library -lblas:
> not found".  I need to investigate this more.

Actually, you did say so... 

Don't worry about error messages like that in config.log; they only
mean that there is no system BLAS and the only way to find out is by
trial and failure. The configure script is full of that sort of code.
 
> 
> > and for gcc 3.4.3 and the internal BLAS (which I had to build for these
> > tests) I get
> > 
> > 32-bit
> > [1]  9.96  0.09 10.12  0.00  0.00
> > 64-bit
> > [1]  9.93  0.04 10.04  0.00  0.00
> > 
> > so I am not seeing anything like the same performance difference between
> > 32- and 64-bit builds (but it could well depend on the particular Sparc
> > chip).
> 
> These timings are much, much less than what I reported (~700s and
> 2200s for 32 bit and 64 bit).  I read the admin manual and didn't see
> anything specifically that needs to be set to use the internal BLAS.  
> I guess I'll go back and do some more investigation.

Yes. If you have hardcore linear algebra needs, those fast-BLAS
speedups can be impressive (Brian might also have a faster machine
than you, mind you). For code that is mainly interpreter-bound, it is
much less so.

While your setup is in place, you might want to play around with the
higher optimization levels. GCC on AMD64 sees a quite substantial
speedup from -O2 to -O3.

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